IPNetwork ignores NOHOST when using copy constructor

```python
>>> IPNetwork('192.0.1.1/24', flags=NOHOST)
IPNetwork('192.0.1.0/24')
>>> IPNetwork(IPNetwork('192.0.1.1/24'), flags=NOHOST)
IPNetwork('192.0.1.1/24')
```

Expected behavior is that the second output returns `IPNetwork('192.0.1.0/24')`.